Six deer species are present in Britain, the native red deer and roe deer and the introduced fallow, sika, muntjac and Chinese water deer. The introduced species either escaped from parks or were deliberately released, giving rise to local naturalized populations. The populations of all species are discontinuous in Britain. Deer are crepuscular (most active near dawn and dusk) and rest for long periods to ruminate. They readily become nocturnal if subject to frequent disturbance.